Two-cycle engine resonance exhaust system

ABSTRACT

Two-cycle engine exhaust systems including a resonance chamber which has at least one change of direction or bend in the resonance chamber and which is used in combination with powered tools and vehicles, such as chain saws and snowmobiles. Bending the resonance chamber saves space and keeps the exhaust resonance chamber out of the way of an operator. The further improvement of including an additional silencing section located within the crook of the bend in the resonance chamber in combination with two-cycle engines, is also disclosed.

United States Patent Tenney [451 May 30, 1972 TWO-CYCLE ENGINE RESONANCE EXHAUST SYSTEM William L. Tenney, Crystal Bay, Minn. 55323 Feb. 9, 1970 Inventor:

Filed:

Appl. No.:

US. Cl ..'.....60/3l4, 60/313, 123/65 E, 123/65 EM, 181/40, 181/53, 181/57 Int. Cl ..F02b 27/04, FOln 5/00 Field 01 Search ..l23/65 E, 65 EM, 179-180; 60/29, 32, 31', 181/36, 36 D, 40, 47, 57

References Cited UNITED STATES PATENTS 5/1968 l-loltermann et a1 ..123/65 1 10/1968 Miller et a1. ..181/4O 3,434,280 3/1969 Burkhart ..60/32 FOREIGN PATENTS OR APPLICATIONS 917,971 2/1963 Great Britain ..60/29 Primary Examiner-Mark M. Newman Attorney-Bugger, Peterson, Johnson & Westman [57] ABSTRACT 24 Claims, 18 Drawing Figures 7 m 26' a T 32 4 i ii 33A 28B I .15"

Patented May 30, 1972 6 Sheets-Sheet l FIE-Z INVENTOR.

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Patented May 30, 19.72 3,565,712

6 Sheets-Sheet 5 I INVEN'I'OR. 1 114M 4 TEA/IVE) M W4Mm A rramvsrs Patented May 30, 1972 3,665,712

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INVILNIUR. l/Al/JM Z. TE/V V'y 1 TWO-CYCLE ENGINE RESONANCE EXHAUST SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-cycle engine exhaust system utilizing exhaust resonance chambers or tuned exhaust systems.

2. Prior Art Several different disclosures of exhaust resonance or expansion chambers for use with two-cycle engines have been advanced in the art. For example,'U.S. Pat. No. 3,385,052 to Holterrnann shows a two-cycle engine exhaust system utilizing a resonating exhaust expansion chamber which operates to obtain a timed return of a pressure wave to the exhaust port. The expansion chamber for obtaining this resonating charac-' teristic is shown in one figure as being doubled back upon it self and in a U form.

One of the problems associated with the use of two-cycle engines is their noise. Even when power increase provided by an expansion chamber exhaust is achieved, the noise can still be quite objectionable. A further problem involved in expansion chamber exhaust systems is the size or length of the presently used expansion chamber that is necessary for operation. In some applications, for example chain saws, the presently available expansion chamber exhaust systems are excessively large and long, and interfere with the operation of the saw itself. The invention disclosed and claimed herein teaches conservation of space in an expansion chamber exhaust system and at the same time discloses structure for obtaining engine silencing without taking more space.

SUMMARY OF THE INVENTION The present invention relates to resonance expansion chamber exhaust systems for use with twocycle engines wherein the expansion chamber has a bend in it. The central axis of the chamber changes direction at least once in order to conserve overall space. At the same time, the bend or curve in the expansion chamber provides an area used for a silencing device, without increasing the external dimensions of the overall external exhaust system, to form a very compact tuned exhaust system using a muffler in certain instances, and an exhaust system that is compact enough for utilization with a chain saw.

It is an object of the present invention to present a tuned or resonance exhaust system having an expansion chamber that has at least one bend or change of direction in the central axis of the expansion chamber.

It is a further object of the present invention to present an expansion chamber exhaust system compact enough for use in combination with chain saws specifically.

It is another object of the invention to present a tuned exhaust system wherein the expansion chamber used with the exhaust system is bent so that the chamber changes direction at least once, andan engine muffler or silencing device is positioned between sections of the chamber in its bent form. The chamber is bent into a curved shape or forms a bend, and the muffler is positioned in the bend and generally within the peripheral confines of the walls of the expansion chamber itself.

A further object of the invention is to provide an expansio chamber exhaust system providing a positive reflected pressure wave at the exhaust port of a two-cycle engine on a chain saw, without causing interference with the handling of the saw.

It is another object of the invention to present an improved expansion chamber exhaust system that can'be manufactured by a casting process and includes a silencing section, if desired.

It is still a further object to present an expansion chamber exhaust system that can be stamped or formed from sheet metal, and includes a silencing section if desired.

Another object is to present an expansion chamber exhaust system provided with ducts for cooling.

LII

It is another object of the present invention to present a chain saw having an expansion chamber exhaust system die cast as part of the engine assembly and which includes a muffler or silencing section, if desired.

Other objects are inherent in the description, and will become apparent as the description proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a chain saw having a twocycle engine showing an exhaust system having an expansion chamber made according to the present invention installed thereon;

FIG. 2 is a bottom plan view of the device of FIG. 1;

FIG. 3 is an end elevational view of the device of FIG. 1;

FIG. 4 is a sectional view taken as on line 4-4 in FIG. 1;

FIG. 5 is a fragmentary sectional view taken as on line 5-5 in FIG. 4;

FIG. 6 is a sectional view taken as on line 6-6 in FIG. 4;

FIG. 7 is a side elevational view of a modified form of attachment of the exhaust system of FIG. 1 showing the exhaust pipe coming over the top of the chain saw housing and leading down to the expansion chamber and further modified in that the expansion chamber is cast partially integral with the chain saw engine itself and has a cover member comprising another part of the expansion chamber and silencing section bolted into place;

FIG. 8 is a fragmentary sectional view taken as on line 8-8 in FIG. 7;

FIG. 9 is a front elevational view of a chain saw having an upright cylinder two-cycle engine showing the connection of an exhaust pipe thereto and showing an expansion chamber exhaust system made according to the present invention installed thereon;

FIG. 10 is a top plan view of the device of FIG. 9;

FIG. 11 is a sectional view taken as on line 11-11 in FIG. 10;

FIG. 12 is a sectional view taken as on line I2l2 in FIG. 1 1;

FIG. 13 is a side elevational view of a further modified exhaust system of the present invention showing a cast construction wherein the resonance chamber and the silencing section are cast, and a cover plate is attached thereto, and the entire unit may be fastened onto the base of a chain saw engine or other two-cycle engine, or may be mounted elsewhere as desired;

FIG. 14 is a sectional view taken as on line 14-14 in FIG. 13;

FIG. 15 is a fragmentary top plan view of a front portion of a snowmobile showing an exhaust system having an expansion chamber such as that shown in FIGS. 13 and 14 installed on the snowmobile engine in a solid line position and in a dotted line position to show alternate positioning of the exhaust chamber;

FIG. 16 is a sectional view of a further modified form of the invention showing a cross section of an expansion chamber and silencing section made by formed metal parts and enclosed to provide cooling ducts between the portions of the unit;

FIG. 17 is a modified form of the invention showing an installation on a two cylinder, two cycle engine; and

FIG. 18 is an end elevational view of the device of FIG. 1 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the description following expansion chamber" and resonance chamber are used interchangeably.

Referring first to FIGS. 1 through 6, a chain saw illustrated generally at 10 is of standard construction and utilizes a single cylinder two-cycle engine 11 that as shown is positioned with the cylinder axis in a substantially horizontal position. The chain saw frame 12 has operator handles 13 and 14. The engine drives a saw chain 15 mounted on a chain bar 16 in the conventional manner of chain saws. The controls for the chain saw also are of the usual type, as is the starting mechanism and centrifugal clutch for the drive to the saw chain.

The two-cycle engine 11 includes a cylinder block 17 which has an internal piston 18 and an exhaust port 19 in the cylinder wall and the engine exhausts in the usual manner. A lead out exhaust pipe 20 is fixed with a flange 21 and suitable cap screws fasten the flange 21 to the cylinder so the exhaust port opens into the exhaust pipe. The exhaust pipe 20 as shown in FIG. 1 extends downwardly and passes around the rear portions of the saw below the rear handle 14. The exhaust pipe enters an expansion chamber housing illustrated generally at 22 and mounted along the bottom of the chain saw. This expansion chamber housing, as shown, comprises a box like member divided into different chambers as will be more fully explained. A planar bottom surface 23 formed by the bottom wall of the housing is used for a stand or platform for the chain saw so that it will rest on this surfacewhen it is not in use. The housing 22, as perhaps best seen in FIGS. 4, and 6, is made so that it is relatively flat, and the main housing comprises a first plate 24, and a second plate 25, as shown, spaced apart in vertical direction (the plate 25 is the bottom plate having surface 23 thereon) and divided into chambers by walls extending between the plates. There is an outer peripheral wall 26 which has a first section 26A along an inlet side of the unit, a second section 2613 which curves around at the forward portion of the housing, and a third section 26C which extends back parallel to section 26A. This forms the outer wall along three sides of the unit. There is an end wall 27 that seals the interior chamber. The exhaust pipe 20 opens through the end wall 27 into the interior chamber of the housrng.

The exhaust expansion chamber is formed in combination with the wall sections 26A, 26B and 26C with an interior divider wall 28 extending between walls 24 and 25. The interior divider wall comprises a first section 28A that is spaced from and diverges with respect to the wall 26A so that it forms a diverging channel of substantially rectangular cross section, as shown in FIG. 6; a curved portion 288 forming in conjunction with the curved portion 26B a wider part of the expansion chamber, and a third section 28C that extends substantially parallel to a portion of the wall section 26C. The walls 26A, 26B and 26C form in combination with the inner walls 28A, 28B and 28C a tubular exhaust expansion or resonance chamber 32 that is bent into a U" shape. The lead in portion of the expansion chamber as shown, diverges, or increases in cross sectional size and is rectangular in cross sectional shape. A transition section 33, which is a complete annular wall, forms a tubular transition converging portion of the rectangular shaped chamber 32 leading into a pipe 34 which has a circular cross section. The pipe 34 is a connection between the expansion chamber 32 and an interior silencing or muffler chamber 35. As shown, the outlet end of pipe 34 is closed with a wall 36, and the pipe has a plurality of apertures or openings 37 through the side wall thereof. It should be noted that the apertures all face generally toward the wall 28C and the transition section 33 (which as previously explained was en closed) so that the hot gases coming from the exhaust port 19 and pipe 20 through the expansion or resonance chamber 32 have to pass through the transition section 33, through the bend of the pipe 34 and out through the aperture 37.

The interior surface 33A of the transition section 33 reduces in cross sectional area from walls 26C and 28C, and this interior surface forms a wave reflecting surface for the pressure waves from the exhaust of the engine thereby fulfilling the function of providing a positive wave reflecting surface that reflects the positive pressure wave back to the exhaust port in accordance with the well known tuned pipe" or resonating pipe principles. The engine silencing or mufiler portion of the assembly further includes an outlet pipe 40 which is, as shown, bent at right angles, and passes through the outer side wall 26 of the assembly. The outlet pipe 40 is sealed at its inner end with a wall 41, but has apertures 42 along the side hereof generally facing wall 28A. Thus, it can be seen that the gases coming from apertures 37 have to travel a sufficient distance across the chamber 35 to enter the apertures 42, causing the exhaust gases to change direction. The outer end 43 of the exhaust gas outlet of the assembly and the discharge is directed, as shown, sideways of the machine so that the operator is not hit by hot gases. The exhaust gases actually deflect around the straight section of the exhaust pipe 20 that is parallel to the bottom plate 25 of theunit. The gases deflecting around the exhaust pipe help to break up and still further reduce the intensity of the sound pressure waves.

As shown, the expansion or resonance chamber 32 expands in cross sectional area from the point of entry of the exhaust pipe into the housing, to a position substantially along a line 32A. The expansion chamber then continues at substantially uniform cross sectional area to the line where the transition section commences. The interior end surface 33A of transition section 33, forms a positive wave reflecting surface that permits the exhaust blow down pressure wave to be reflected back through the chamber 32, the exhaust pipe, and back to the exhaust port 19 while this port is still open thereby to minimize loss of fresh charge gases out of the engine cylinder. This positive wave reflecting surface thus serves to reflect sound pressure wave energy back toward theengine exhaust port instead of out into the open air. The wave reflecting surface thus acts to reduce the sound level of the engine, and serves this function in all forms of the invention. Further, the positioning of theapertures so that the exhaust gases have to change direction at least two times before they are discharged out through the pipe 40 tends to cool and arrest sparks from the exhaust gas before it is discharged. If a further baffle or other means is desired at the outlet end 43 of pipe 40 for spark arresting or additional silencing, it can be provided.

With further reference to the expanding portion of chamber 32, it should be pointed out that this portion of the chamber also serves an important function in increasing the power output from the engine. Passage of the exhaust blow down pressure wave through this expanding section causes a negative pressure wave to be reflected back to the engine exhaust port. This causes a negative pressure at the engine exhaust port during the scavenging phase to increase power by aiding the scavenging process. The positive pressure wave reflected by the converging end of the chamber arrives at the exhaust port at the end of the scavenging process and still further increases the engine power output, as described above.

The use in a chain saw of the curvedor bent expansion chamber exhaust without an additional silencing section also can be advantageous because of the very compact configuration that the curved expansion chamber makes. If no additional silencing or muffler section is desired, the transition section 33 and pipe 34 would merely discharge into the atmosphere, and if desired, through a suitable tubular outlet rather than using the silencing section. The tubular outlet also has some effect on the engine power output. The positive wave reflecting surface 33A would still be provided, to pro vide the positive reflected pressure wave, and the expansion chamber is made so the principal exhaust waves reach resonance at the desired speed of the engine to increase the engine power because of the advantages of having the positive reflected wave. Thus, the concept disclosed here also includes omission of the separate silencing section and use of a bent expansion chamber mounted on a chain saw.

When the silencing section is not utilized, the space in the crook or bend of the expansion chamber walls can be used for other things, for example the entire expansion chamber housing can be mounted on the top of the chain saw and the space of chamber 35 can be utilized for a chain oiler space, for oiling the chain of the saw. In all forms shown, the expansion chamber assembly can be mounted on the front, rear, sides, top or bottom of the chain saw.

The use of a resonance chamber or expansion chamber in the exhaust system is presently known. The resonant speed of an expansion chamber exhaust system is dependent upon many factors including principally the timing of the engine exhaust port, the distance from the reflecting surface to the exhaust port, and the temperature of the exhaust gases.

In the final analysis there is a requirement that there be a diverging chamber section in direction away from the exhaust port that the system is connected to, and a wave reflecting surface between the divergingsection and the outlet from the chamber to provide for positive pressure wave reflection.

The use of lead in exhaust pipes as shown in the drawings, is convenient for locating the expansion chamber at some position remote from the exhaust port. However, the diverging portion of the chamber can commence right at the exhaust port, if desired.

The use of a muffler or silencing section has been shown to be advantageous not only from the standpoint of noise reduction, but also in some instances has further improved engine performance to some degree. For example, in chain saw applications the addition of a silencing section has appeared to improve the lugging power. It is theorized that power increasing effects of this nature may be due to resonance or back pressure effects existing in the muffler section which can assist the action of the power increasing expansion chamber section. In general, however, the power increasing effect of chambers downstream from the power increasing expansion chamber are of a comparatively small magnitude.

The concept of placing at least a 90 change of direction in the tubular chamber into a U" shape (180 bend) provides the desired reduction of overall length and provides a convenient and space saving place to put in additional engine silencing devices.

In FIGS. 7 and 8, a modified showing of the chain saw 10 utilizing a different construction of the expansion chamber housing is shown. In this form, the chain saw 10, which is of the same design as before, uses an exhaust pipe 45 that has a flange 46 attached to the cylinder and open to the exhaust port, as in the first form of the invention, but this exhaust pipe 45 passes upwardly over the top of the saw, underneath the handle 13, and then down vertically along side the saw chain to reach the expansion chamber-silencing device assembly housing 47. The housing 47 is of a unique form and the upper portion is actually die cast integral with the bottom of the block 48 for the chain saw engine assembly. The housing 47 is divided into an upper section 49 which is integral with the block 48 and lower section or cover 49A. The upper section has defined therein the upper half of the expansion chamber 50. The expansion chamber 50 curves around one end of the machine. The direction of extension is reversed from expansion chamber 32. The exhaust here is introduced at the end of the assembly adjacent the chain saw bar, rather than at the opposite end. There is an inlet side 50A, and an outlet side 50B of the expansion chamber. The outlet side 50B of the expansion chamber has a wave reflecting surface corresponding to the interior surface 33A, cast into the block, and suitable openings open from the chamber section 508 into a first silencing section passageway 51. The first silencing section passageway 51 is formed with divider walls 51A cast into the bottom portion 49A. Suitable openings or apertures 52 are provided in the divider wall forming the passageway 51 and the gases pass through openings or apertures 53 in a divider wall 54A cast into the top portion 49 of the housing which forms an outlet passageway 54. Outlet pipe 54 serves the same function as the outlet pipe 40. Sealing cover walls 51B and 54B are provided and are suitably sealingly held in place to close passageways 51 and 54 off from each other, and also close them 05 from the chamber 50 except for the passage through the apertures. The covers 518 and 54B can be attached in place after casting the parts or could be cast in place by utilizing collapsible core dies. Note that portions of the inner divider walls forming the expansion chamber sections 50A and 50B seal on the cover walls 51B and 548 where required.

The sections 49 and 49A are provided with flange portions 55, that can be bolted together with small cap screws or bolts to hold the two sections together. The sections 49 and 49A can be gasketed where they mate, if desired. The outlet chamber or pipe 54 discharges into the atmosphere, and the apertures 52 and 53 provide for silencing as in the first form of the invention. The die casting can be done quite cheaply because the main engine assembly castings now made for twocycle engines used in chain saws are usually die cast, and merely by providing a proper cover 49A, the units can be economically made.

. In FIGS. 9, 10, 11 and 12 a modified form of the invention is shown installed on a chain saw 60 that has an engine 61 with an upright cylinder, and having a piston that moves in up and down direction. The engine has a cylinder housing 62, with a piston of conventional design, shown fragmentarily at 63, and an exhaust port 64 defined in the cylinder wall. The engine operates in conventional two-cycle chain saw style, and has suitable clutch mechanism for the drive to the chain saw, as well as starting mechanism. A chain bar 65 is mounted onto the saw, and a cutting saw chain 66 is mounted on the chain bar and driven from the engine 61 through a centrifugal clutch in a conventional manner. The saw as shown also has a forward handle 67, and a saw grip 68 at the rear of the unit.

An exhaust pipe 71 is attached with a flange 72 to the cylinder wall, and the exhaust pipe is open to port 64 and therefore to the interior of the cylinder of the engine 61. The exhaust pipe as shown on this upright engine comes out at the forward side of the engine, and curves downwardly, to open into an expansion chamber-silencing section housing illustrated generally at 73. The saw has a chain oiler tank 74 that has a recess defined therein so that the exhaust pipe can pass down through this recess into the housing 73.

The housing 73 is mounted onto the bottom of the chain saw 60, as shown, in any suitable manner, and includes a top wall member 76, a substantially parallel bottom wall member 77 and suitable divider walls extending between the walls 76 and 77 to form the desired chambers. For example, referring to FIGS. 11 and 12, there is a lead in transition section 80 which leads from the round exhaust pipe 71 into the interior of the housing 73 which has a rectangular cross section chamber. An outer wall 81 has a first section 81A, leading from the transition section 80, a second curved end section 81B, and a third straight section 81C opposite from section 81A. An interior wall 82 is used in combination with the walls 76 and 77 and the wall 81 to form an expansion or resonance chamber 83. The wall 82 includes a first section 82A, that joins the transition section 80, and this wall 82A in combination with the wall 81A forms a first section of the expansion chamber 83 having an expanding cross sectional area. The expanding portion of the chamber causes a negative reflected pressure wave with the benefits described in the first form of the invention. The wall 82 has a curved section 82B, cooperating with the curved section 81B, and a straight section 82C that is substantially parallel to the straight section 81C to form the outlet end portion of the expansion chamber.

The chamber 83 expands in cross sectional area up to about line 83A. The expansion chamber then continues at substantially uniform cross sectional area to its junction with a tubular outlet transition section 84.

The tubular outlet transition section 84 extends from the walls 81C and 82C, and tapers in a reducing cross sectional area toward an outlet pipe 85. The outlet pipe 85 is circular in cross section, and the transition section 84 goes from rectilinear cross section to circular to mate with this pipe 85. Actually, the curved portion 85A of the pipe 85 can be conical and reducing in cross sectional area until it gets out into the main portion of the pipe 85, if desired. The interior surface The pipe 85 opens into a silencing chamber 90 that is defined by the walls 82A, 82B and 82C and the walls 76 and 77. The chamber is sealed with a suitable end wall, for example the end wall 91 to form the chamber 90. The end wall 91 as well as the walls 76 and 77 can be trimmed or bent as desired to seal along the transition section 84, and completely close the chamber 90 except for the inlet through the expansion chamber and apertures 86, and an outlet through apertures 92 defined in an outlet pipe 93 that is mounted in the chamber 90. The outlet pipe 93 has an end wall 93A to block the inner end, and discharges to the front, as shown. A small end portion 94 protrudes out beyond the wall 91. The exhaust gas discharges at the forward end of the saw and in forwardly direction, thereby keeping the exhaust away from the operator. The exhaust gas discharge can be used to blow sawdust away. Suitable baffles can be provided on the outlet of the exhaust for directing the exhaust blast wherever it is desired and to the direction of flow of gases from the exhaust port. In other words, the wave reflecting surface is generally transverse to the direction of movement of gases through the expansion chamber. When the term positive wave reflecting surface" is used, it means not only the converging surfaces as shown, but

' also possible transverse surfaces which will provide forthe positive reflected wave back at the exhaust port at the proper time when the speed of resonance has been reached by the engme.

The separate silencing section, again, quiets the noise from the engine and is nestled in the area between the inlet and outlet end sections'of the expansion chamber'to conserve space, and to have the muffler or silencing section utilize previously unused space. The curved expansion chamber 'conserves space as well so that the device can be utilized on chain saws and other hand powered implements using two-cycle engines. The small, compact design is also suitable for vehicular use.

A modified form of the housing is shown in FIGS. 13 and 14. The expansion chamber-silencing section housing 96 is substantially the same as the housing on the chain saw 60. The top of the housing can be mounted on the bottom or other side or top surface of a chain saw or. in any desired location. An exhaust pipe 98 from a two-cycle engine, for example engine 61, leads into the housing 96. This particular housing 96 is a cast housing having a main section 99, and a cover plate 100. In certain instances, the cover plate is not necessary, and the entire main section 99 can be simply bolted against the bottom surface of the main assembly of a chain saw or the like. In other applications, as will appear in FIG. when this figure is discussed, the use of a cover plate makes this a unit that can be positioned conveniently in any location.

Referring now specifically to FIG. 14, the housing 96 is cast with walls again forming a power increasing expansion chamber and silencing section. Suitable lugs or cars are provided for fastening the cover plate 100 into place with countersunk screws, as shown. The walls include an outer wall 103 again made up of a first section 103A, a curved. section 103B, and an outlet end section 103C. An interior partition wall 104 includes a first section 104A near the inlet pipe 98, a curved section 104B opposite the section 1038 and an outlet end section 104C which is relatively short as shown. The walls 103 and 104 form a tubular expansion chamber 105 that is curved (changes direction) and there is a space between the walls 104A and 104C that comprises a silencing section chamber. The chamber here also forms a U shape.

At the ends of walls 104C and 103C, there is a converging transition secton 106, comprising a wall 107 tapering toward an extension of wall 103C to form a positive wave reflecting surface 107A. This surface is on the side of the wall 107 facing the wall 103C. The end section does not decrease in size in vertical direction, or in other words between the bottom wall and the cover plate, but decreases in size in transverse direction to provide the'wave reflecting surface 107A. Also, at

adjacent wall 108 of the housing, a passageway is formed where the gases change direction, .and a portion of the inner surface 108A of the wall 108 forms another part of the positive wave reflecting surface, to provide resonance at the engine speed desired.

A divider wall 1 10 is provided on the interior of the housing substantially parallel to the wall 107 to form a chamber 111. The wall 1 10 has apertures 1 12 defined therethrough, through which the hot gases coming from the expansion chamber will pass to help suppress of silence the noise from the engine, and the gases pass into a chamber 113 formed by a wall 110 and a second wall 114. The chamber 111 serves the same function as the first outlet pipe 34 in the first form of the invention, and the outlet pipe 85 in the second form of the invention shown in FIG. 12. The wall 114 has a plurality of apertures 115 defined therethrough, and this plurality of apertures permit the hot gases to pass through the chamber 113 into a chamber 116 formed between the wall 114 and the wall section 104A and a portion of the section 1048. This is the final stage of the silencing section, and as can be seen an outlet pipe 120 sealingly passes through a portion of the wall 108, and the end of this pipe 120 is blocked with a wall 121 at its inner end. The pipe 120, however, is provided with apertures 122 on one side thereof so that the gases coming through the apertures 115 pass into the chamber 116, expand, and then have to pass through the openings or apertures 122 into the interior pipe 120 before being exhausted out through the end portion of the pipe 120 that extends outwardly beyond the wall 108.

Thus, in FIG. 14 is can be seen that the separate silencing section actually comprises the chambers and walls between wall 104 and wall 107 which define the primary expansion chamber and wave reflecting surface. Therefore, the concept of having the silencing section nestled in an area between the walls of a curved or bent expansion section is carried out with the cast housing that can be easily made, economically installed, and used in a wide variety of applications.

As shown in dotted lines in FIG. 14 an alternate positive wave reflecting surface can be provided through the use of a partially curved transverse wall 109. An aperture 109A, also shown in dotted lines, would permit the exhaust gases to escape out into the separate silencing section of the housing but the surface of the wall 109 facing back toward the inlet to the expansion chamber would provide for this positive wave reflecting surface instead of the wall 107 and surface 107A. The criteria of having a reflecting surface that is transverse to the generaldirection of exhaust gas flow is met by either surface 107A or the surface of wall 109. Various wall shapes will serve to provide the positive wave reflecting surface. The aperture 109A can take other forms, if desired, for instance, a slot or multiple smaller apertures, etc.

In FIG. 15 the housing or expansion chamber-silencing section assembly such as that shown at 96 is shown installed on a snowmobile. The snowmobile 125 is provided with front skis 126 as is customary, and a frame 127. A two-cycle engine 128, as shown here a single cylinder engine having an output clutch and variable ratio drive pulley 129 for driving the snowmobile, is mounted at the forward portion of the snowmobile as is customary. The engine 128 has an exhaust outlet, and an exhaust pipe 130 is attached to the cylinder housing 131 of the engine. The exhaust pipe has a metal flexible tube 132 sealingly attached thereto to permit the tube to curve around portions of the engine. The housing 96 comprising the expansion chamber and muffler or silencing section is mounted onto the side surface orside portions of the snowmobile adjacent the engine, out of the way. The exhaust is preferably discharged downwardly through the body pan of the snowmobile, outside of the engine compartment.

A dotted position of the housing 96 is shown at the front of the engine, where there would be cooling air available for cooling the expansion chamber and exhaust system if desired, and it can be seen that the housing 96 can conveniently be placed on either side of the engine, above it, or in front of it as desired. The compact expansion chamber does not need a long pipe extending rearwardly along the operators area which is to the rear of the engine, thus avoiding the problems that could arise because of a hot expansion chamber burning the operator. Of course, any of the previous forms of the invention can be used with a snowmobile merely by making a proper mounting bracket. The use of a silencing section in snowmobiles is very advantageous because one of the objections that arises when use of snowmobiles is discussed is the noise they cause and the consequent adverse publicity that is created.

In FIG. 16 a typical cross sectional view is taken across a unit embodying the principles of the invention but made of a formed or stamped sheet metal housing. The unit illustrated generally at 135 comprises a first section 136 and a second section 137 which are substantially mirror images of each other and have flanges 138 that are joined together in a suitable manner, for example by seam welding, so that the two sections are sealed together. The sections 136 and 137 together form the inlet portion 140 of an expansion chamber, an outlet portion 141 of an expansion chamber (the chamber curves around as in the previous forms of the invention) and a silencing or muffler secton 142. There are wall portions 143 between the inlet portion 140 and the silencing section 142, and walls 144 between the silencing section 142 and the outlet portion 141. Suitable passageways are provided between the outlet portion 141 of the expansion chamber and the silencing section 142. The passageway, as shown, comprises a tube or pipe 145 that opens into the outlet portion 141 and is suitably fastened in place. The pipe 145 has apertures 146 defined therein. An outlet pipe 147 is also provided in the silencing chamber 142. The outlet pipe 147 has apertures 148 defined therein, and the outlet pipe leads to the exterior of the housing, just as the outlet pipe in the previous forms of the invention does. The outlet pipes can be welded in place, if desired.

The wall portions 143 and 144 form depressions between the individual sections, and cover walls 150 and 151 can be provided to seal off these depression areas to form channels 152, 153, 154 and 155. These channels formed by the walls 150 and 151 can have air or fluid inlet or outlet so that these will form cooling channels for the side surfaces of the silencing section 142, and the inlet and outlet portions of the expansion chambers. This fluid could be cooling air from the atmosphere if the housing is on a moving vehicle such as a snowmobile, or could be fan driven air blown through to effect cooling if desired. The stamped or formed metal sections are readily made with the use of dies and welding the sections together to seal the various chambers makes quick construction. In plan view the housing looks substantially like that in FIG. 4 except there are the wall portions 143 and 144 between the expansion chamber section and the silencing section which is centrally located. The unit would be provided with a positive wave reflecting surface on the outlet portion of the expansion chamber.

The same principles are involved here except cooling is added by having ducts or channels between the expansion chamber sections and the silencing chamber section. It can also be seen that if desired the housing can be made with only the U-shaped expansion chamber merely by eliminating the center silencing chamber 142. The outlet end of the expansion chamber then would lead to the exterior of the housing.

Of course, cooling ducts can be provided on any of the previous forms of the invention by having double walls forming ducts for cooling.

Referring now to FIGS. 17 and 18, a further modification of the present invention is illustrated with reference to a two cylinder two-cycle engine 158.

As shown, a first cylinder 159 and a second cylinder 160 are mounted side by side onto a common engine housing, and

each has an exhaust outlet leading to separate exhaust pipes 161 and 162, respectively. The exhaust pipes 161 and 162 each lead into a separate tubular expansion chamber housing 163 and 164, respectively. As shown, the expansion chamber housings each have diverging or expanding inlet sections 163A and 164A. The chamber housings curl around like a rams horn or scroll, around a tubular member 165 forming a muffler or silencing chamber. The end portions 166 of the two chamber housings 163 and 164, as shown in FIG. 18, converge to form separate wave reflecting surfaces on the interior of the chambers. The expansion chambers open into the interior of the member 165 which is a common separate silencing chamber or muffler used for both of the expansion chambers. The muffler has an outlet pipe 167 leading therefrom. Baffles or other silencing arrangements inside the muffler can be provided as desired. Pipes such as those illustrated in the previous forms of the invention having apertures for inlet and outlet can be utilized if desired as well. The length of the expansion chambers can be made sufficiently great to provide for resonance at the desired frequency because of the scroll or rams horn shape of the expansion chamber. It can be seen that the expansion chambers are again bent to provide for an area into which the silencing chamber 165 can be placed. This can be done either with single cylinder engines or multi-cylinder engines as desired.

The silencing chambers shown in all forms have low back pressure in order not to interfere with operation of the power increasing expansion chambers.

In terms of power increase, an ordinary sound absorbing muffler will reduce the power of a typical crankcase scavenged two-cycle engine by at least 5 too 10 percent. The devices shown, using silencing chambers, are as quiet or quieter than the ordinary sound absorbing muffler supplied with two-cycle engines. In addition, a resonance chamber or expansion chamber is capable of easily increasing the power of a crankcase scavenged two-cycle engine in the range of 20 to 25 percent without any change in design of the engine itself. This results in a total power increase over conventionally silenced engines of between 25 and 35 percent and has been proved by actual dynamometer tests. Space is saved, power is increased, and all of the advantages of both a muffler and a tuned exhaust are present.

The weight of the devices can be held to a minimum. Aluminum chamber housings which can be cast are very light, weighing in the general range of from 1 pound to 1% pounds for chain saws, and thus it can be seen that with a small weight increase of approximately 5 to 10 percent on alight chain saw, a power increase of from 25 to 35 percent is available. Also, better silencing is possible with the construction of the present invention.

It should be again mentioned that the mounting of the expansion chamber-silencing chamber assembly can be in any desired position, such as on the bottom, as shown, the top or on the sides of the engine on which it is used.

The diverging or converging sections of the power increasing expansion chamber can be made with stepped or irregular surfaces instead of the smooth surfaces shown without departing from the teaching of the invention.

The term tubular as used to describe the channels of the various chambers means hollow conduit channels of any desired cross sectional shape, such as circular, elliptical or rectilinear.

The silencing sections, instead of, or in combination with the perforated pipes shown, can use glass fiber packed chambers, steel wool packed chambers or other conventional silencing means.

It should be recognized that a single expansion chamber may be used for more than one engine cylinder in instances if proper lead in pipes are provided.

The expansion chamber units shown in FIGS. 1-16 all are substantially planar. However, bending or forming the housings transversely or longitudinally in many instances is desirable to fit around engine parts or into small places. For example, the device of FIG. 6 could be curved in cross section, rather than planar, forming a transverse curve. The device of FIG. 13 could be curved in this view and thereby form a longitudinal curve. Compound curves of the housings are also possible.

The generally expanding lead in portions of the expansion chambers also can be placed outside of the housings or boxes, and the lead in expanding sections can be curved to fit around comers. For example, in FIG. 4 in place of the lead in pipe 20, the expanding section would extend around the bend of pipe 20 shown at the upper left-hand corner of this figure. Thus the expanding section would be outside the boxed in assembly and also would be bent or curved.

What is claimed is:

1. In a chain saw engine exhaust system, said engine having an exhaust port, the improvement comprising a resonant chamber exhaust for said chain saw engine leading from the exhaust port on the engine including a tubular member having an inlet and an outlet and a first diverging section generally expanding in cross sectional area to a cross sectional area greater than the area of said exhaust port, a positive exhaust gas pressure wave reflecting surface in said tubular member between said first diverging section and the outlet of said tubular member, means positioning said positive exhaust gas pressure wave reflecting surface so as to reflect the principal exhaust gas pressure wave back to said exhaust port for arrival at said exhaust port shortly prior to closing of said exhaust port when the engine revolution per minute is in a desired range, said tubular member being bent into a shape so the outer peripheral dimensions thereof are not substantially greater than the outer peripheral dimensions of the main body of said chain saw, and an engine exhaust silencing means substantially within the confines of the periphery of the bent tubular member and open to the outlet of the tubular member.

2. The combination as specified in claim 1 wherein said tubular member is formed at least partially with substantially coextensive top and bottom walls, and divider walls forming the diverging section and the wave reflecting surface between said top and bottom walls, one of said top and bottom walls being substantially contiguous with the chain saw.

3. The combination as specified in claim 1 wherein said tubular member is formed at least partially into the engine portion of said chain saw.

4. The combination as specified in claim 1 wherein said positive wave reflecting surface is formed by a generally converging surface between an outer end of said diverging section and the outlet from said tubular member.

5. The combination as specified in claim 1 wherein said tubular member is formed at least partially with generally coextensive spaced apart first and second walls, and divider walls forming the diverging section and the wave reflecting surface extending between said first and second walls, one of said first and second walls being substantially contiguous with the chain saw.

6. The combination as specified in claim 1 wherein said tubular member is bent generally into a U shape forming a pair of legs, said engine exhaust silencing means being positioned between the legs of the U shaped tubular member.

7. The combination as specified in claim 1 wherein there is provided a die cast exhaust housing which includes said tubular member and silencing sections and which has substantially parallel spaced apart main walls, divider walls extending between said main walls, and means removably fastening one of the main walls to the remainder of said housing.

8. The combination as specified in claim 7 wherein said divider walls are positioned relative to each other so that the tubular member has a curved portion and two end portions formed in the general shape of a U, said curved portion being part of the first diverging section of said tubular member.

9. In a two-cycle internal combustion engine having a power cylinder and exhaust port, the improvement comprising an exhaust system including a tubular member comprising walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said outlet being of reduced area as compared with the maximum cross sectional area of said first section, said second section forming a positive exhaust gas pressure wave reflecting surface, means positioning said second section so as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port for arrival at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, said tubular member having at least one bend along its length to form a shape for said tubular member other than linear, said tubular member walls thereby having peripheral surface portions which at least partially define a space other than said chamber, and means defining an exhaust silencing section separate from said chamber confined substantially within the space defined by the peripheral surface portions of said tubular member, the outlet of said chamber opening to said silencing section, and said silencing section having exhaust gas discharge means.

10. The combination as specified in claim' 9 wherein said generally expanding cross section of said expansion chamber expands to a cross sectional area greater than the cross sectional area of the exhaust port of said internal combustion engine.

11. The combination as specified in claim 9 wherein said tubular member has first and second walls which have general planes that extend parallel for at least portions thereof, ad divider walls extending between said first and second walls forming the first, second and silencing sections, and removable means fastening the first wall for said tubular member to a main portion thereof.

12. The combination as specified in claim 9 wherein the central axis of said tubular member changes direction at an included angle of at least so that portions of the walls of the tubular member face generally toward each other, at least a portion of said silencing section being positioned between the portions of the walls of said tubular member that face generally toward each other. i

13. The combination as specified in claim 12 wherein said silencing section is generally cylindrical, said tubular member being of length to wrap at least partially around said silencing section.

14. The combination as specified in claim 12 wherein said internal combustion engine has a plurality of power cylinders each with an exhaust port, a separate tubular member leading from the exhaust port for each cylinder, said silencing section being a generally cylindrical member, said separate tubular members being wrapped at least partially around said generally cylindrical member and each opening to said generally cylindrical silencing section.

15. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including a tubular member having walls forming an exhaust chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second section including means forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port and arriving at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, the central axis of said tubular member changing direction at least once to form a shape for said tubular member other than linear, and an exhaust silencing section confined substantially within the extremities of the peripheral dimensions of said tubular member, the outlet of said exhaust chamber opening to said silencing section, said silencing section comprising a closed silencing chamber, a first passageway means leading from said second section and being open to said silencing chamber, said first passageway means being blocked at the end thereof in said silencing chamber and having perforations therethrough positioned in said silencing chamber, and an exhaust gas outlet pipe open to said silencing chamber and the exterior of said exhaust system, said outlet pipe having the end thereof blocked on the interior of said silencing chamber and being provided with perforations through a side wall thereof.

16. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including a tubular member having walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second section including means forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port and arriving at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, the central axis of said tubular member being bent substantially into a U shape with the bend portion of said tubular member in a generally expanding portion of said chamber, and an exhaust silencing section confined substantially within the extremitiesof the peripheral dimensions of said bent tubular member, the outlet of said chamber opening to said silencing section, and exhaust gas discharge means from said silencing section.

17. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including a tubular member having walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional areain direction away from said exhaust port, a second section open to the first section and the outlet, said second section including means forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port and arriving at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, said tubular member being formed into a generally U shaped member, and an exhaust silencing section positioned between the facing walls of said tubular member forming the U, the outlet of said chamber opening to said silencing section, and exhaust gas discharge means from said silencing section.

18. The combination as specified in claim 17 wherein said tubular member and said silencing section are spaced, and wall means defining fluid passageways between portions of said tubular member and said silencing section.

19. The combination of claim 17 further characterized in that the tubular member is made from sections of formed sheet metal, said silencing section being spaced from the walls forming the tubular member and substantially planar wall means joining the walls of said tubular member and said silencing section.

20. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including a tubular member having walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second section including generally converging surface means located between an outer end of said first section and the outlet from said chamber and forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave to arrive back at the engine exhaust shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, the central axis of said tubular member changing direction at least once to form a shape for said tubular member other than linear, and an exhaust silencing section confined substantially within the extremities of the peripheral dimensions of said tubular member, the outlet of said chamber opening to said silencing section, and exhaust gas discharge means from said silencing section.

21. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including a tubular member having walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second sec tion including means forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port and arriving at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, said tubular member including first and second wall means that overlie each other and are generally coextensive, and divider wall means extending between said first and second wall means, said wall means forming the first section and the wave reflecting surface, the central axis of said tubular member changing direction at least once to form a shape for said tubular member other than linear, and an exhaust silencing section confined substantially within the extremities of the peripheral dimensions of said tubular member, the outlet of said chamber opening to said silencing section, and said silencing section having exhaust gas discharge means.

22. The device of claim 21 further characterized in that said tubular member is formed into two parts, said first wall means and said divider wall means being integrally formed together, and said second wall means being removably fastened with respect to said divider wall means.

23. Said device of claim 21 wherein said divider wall means are positioned relative to each other so that the tubular member is formed into the general shape of a U, and said exhaust silencing section is positioned between the divider wall means forming the facing sides of the legs of the U shaped tubular member.

24. The device of claim 21 wherein said divider wall means are of substantially smaller height than the width and length of said first and second wall means. 

1. In a chain saw engine exhaust system, said engine having an exhaust port, the improvement comprising a resonant chamber exhaust for said chain saw engine leading from the exhaust port on the engine including a tubular member having an inlet and an outlet and a first diverging section generally expanding in cross sectional area to a cross sectional area greater than the area of said exhaust port, a positive exhaust gas pressure wave reflecting surface in said tubular member between said first diverging section and the outlet of said tubular member, means positioning said positive exhaust gas pressure wave reflecting surface so as to reflect the principal exhaust gas pressure wave back to said exhaust port for arrival at said exhaust port shortly prior to closing of said exhaust port when the engine revolution per minute is in a desired range, said tubular member being bent into a shape so the outer peripheral dimensions thereof are not substantially greater than the outer peripheral dimensions of the main body of said chain saw, and an engine exhaust silencing means substantially within the confines of the periphery of the bent tubular member and open to the outlet of the tubular member.
 2. The combination as specified in claim 1 wherein said tubular member is formed at least partially with substantially coextensive top and bottom walls, and divider walls forming the diverging section and the wave reflecting surface between said top and bottom walls, one of said top and bottom walls being substantially contiguous with the chain saw.
 3. The combination as specified in claim 1 wherein said tubular member is formed at least partially into the engine portion of said chain saw.
 4. The combination as specified in claim 1 wherein said positive wave reflecting surface is formed by a generally converging surface between an outer end of said diverging section and the outlet from said tubular member.
 5. The combination as specified in claim 1 wherein said tubular member is formed at least partially with generally coextensive spaced apart first and second walls, and divider walls forming the diverging section and the wave reflecting surface extending between said first and second walls, one of said first and second walls being substantially contiguous with the chain saw.
 6. The combination as specified in claim 1 wherein said tubular member is bent generally into a U shape forming a pair of legs, said engine exhaust silencing means being positioned between the legs of the U shaped tubular member.
 7. The combination as specified in claim 1 wherein there is provided a die cast exhaust housing which includes said tubular member and silencing sections and which has substantially parallel spaced apart main walls, divider walls extending between said main walls, and means removably fastening one of the main walls to the remainder of said housing.
 8. The combination as specified in claim 7 wherein said divider walls are positioned relative to each other so that the tubular member has a curved portion and two end portions formed in the general shape of a U, said curved portion being part of the first diverging section of said tubular member.
 9. In a two-cycle internal combustion engine having a power cylinder and exhaust port, the improvement comprising an exhaust system including a tubular member comprising walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said outlet being of reduced area as compared with the maximum cross sectional area of said first section, said second section forming a positive exhaust gas pressure wave reflecting surface, means positioning said second section so as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port for arrival at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, said tubular member having at least one bend along its length to form a shape for said tubular member other than linear, said tubular member walls thereby having peripheral surface portions which at least partially define a space other than said chamber, and means defining an exhaust silencing section separate from said chamber confined substantially within the space defined by the peripheral surface portions of said tubular member, the outlet of said chamber opening to said silencing section, and said silencing section having exhaust gas discharge means.
 10. The combination as specified in claim 9 wherein said generally expanding cross section of said expansion chamber expands to a cross sectional area greater than the cross sectional area of the exhaust port of said internal combustion engine.
 11. The combination as specified in claim 9 wherein said tubular member has first and second walls which have general planes that extend parallel for at least portions thereof, ad divider walls extending between said first and second walls forming the first, second and silencing sections, and removable means fastening the first wall for said tubular member to a main portion thereof.
 12. The combination as specified in claim 9 wherein the central axis of said tubular member changes direction at an included angle of at least 90* so that portions of the walls of the tubular member face generally toward each other, at least a portion of said silencing section being positioned between the portions of the walls of said tubular member that face generally toward each other.
 13. The combination as specified in claim 12 wherein said silencing section is generally cylindrical, said tubular member being of length to wrap at least partially around said silencing section.
 14. The combination as specified in claim 12 wherein said internal combustion engine has a plurality of power cylinders each with an exhaust port, a separate tubular member leading from the exhaust port for each cylinder, said silencing section being a generally cylindrical member, said separate tubular members being wrapped at least partially around said generally cylindrical member and each opening to said generally cylindrical silencing section.
 15. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including a tubular member having walls forming an exhaust chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second section including means forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port and arriving at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, the central axis of said tubular member changing direction at least once to form a shape for said tubular member other than linear, and an exhaust silencing section confined substantially within the extremities of the peripheral dimensions of said tubular member, the outlet of said exhaust chamber opening to said silencing section, said silencing section comprising a closed silencing chamber, a first passageway means leading from said second section and being open to said silencing chamber, said first passageway means being blocked at the end thereof in said silencing chamber and having perforations therethrough positioned in said silencing chamber, and an exhaust gas outlet pipe open to said silencing chamber and the exterior of said exhaust system, said outlet pipe having the end thereof blocked on the interior of said silencing chamber and being provided with perforations through a side wall thereof.
 16. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the imprOvement comprising an exhaust system including a tubular member having walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second section including means forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port and arriving at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, the central axis of said tubular member being bent substantially into a U shape with the bend portion of said tubular member in a generally expanding portion of said chamber, and an exhaust silencing section confined substantially within the extremities of the peripheral dimensions of said bent tubular member, the outlet of said chamber opening to said silencing section, and exhaust gas discharge means from said silencing section.
 17. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including a tubular member having walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second section including means forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port and arriving at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, said tubular member being formed into a generally U shaped member, and an exhaust silencing section positioned between the facing walls of said tubular member forming the U, the outlet of said chamber opening to said silencing section, and exhaust gas discharge means from said silencing section.
 18. The combination as specified in claim 17 wherein said tubular member and said silencing section are spaced, and wall means defining fluid passageways between portions of said tubular member and said silencing section.
 19. The combination of claim 17 further characterized in that the tubular member is made from sections of formed sheet metal, said silencing section being spaced from the walls forming the tubular member and substantially planar wall means joining the walls of said tubular member and said silencing section.
 20. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including a tubular member having walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second section including generally converging surface means located between an outer end of said first section and the outlet from said chamber and forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave to arrive back at the engine exhaust shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, the central axis of said tubular member changing direction at least once to form a shape for said tubular member other than linear, and an exhaust silencing section confined substantially within the extremities of the peripheral dimensions of said tubular member, the outlet of said chamber opening to said silencing section, and exhaust gas discharge means from said silencing section.
 21. In a two-cycle internal combustion engine having a power cylinder and an exhaust port, the improvement comprising an exhaust system including A tubular member having walls forming a chamber having an inlet and an outlet, and including a first section generally expanding in cross sectional area in direction away from said exhaust port, a second section open to the first section and the outlet, said second section including means forming a positive exhaust gas wave reflecting surface so positioned as to reflect the principal positive exhaust gas pressure wave back to the engine exhaust port and arriving at said exhaust port shortly prior to closing of said exhaust port when the engine revolutions per minute are in a desired range, said tubular member including first and second wall means that overlie each other and are generally coextensive, and divider wall means extending between said first and second wall means, said wall means forming the first section and the wave reflecting surface, the central axis of said tubular member changing direction at least once to form a shape for said tubular member other than linear, and an exhaust silencing section confined substantially within the extremities of the peripheral dimensions of said tubular member, the outlet of said chamber opening to said silencing section, and said silencing section having exhaust gas discharge means.
 22. The device of claim 21 further characterized in that said tubular member is formed into two parts, said first wall means and said divider wall means being integrally formed together, and said second wall means being removably fastened with respect to said divider wall means.
 23. Said device of claim 21 wherein said divider wall means are positioned relative to each other so that the tubular member is formed into the general shape of a U, and said exhaust silencing section is positioned between the divider wall means forming the facing sides of the legs of the U shaped tubular member.
 24. The device of claim 21 wherein said divider wall means are of substantially smaller height than the width and length of said first and second wall means. 